Method and system for analyte determination

The invention relates to methods, kits and systems for determining an analyte in a liquid sample as well as the use thereof for concentration analysis and screening purposes. In one method, a specific binding partner to the analyte is permitted to compete with a conjugate containing the analyte or an analyte analogue for the binding to free analyte. The conjugate also contains a component that specifically binds to a solid support so that reacted and unreacted conjugate are bound thereto when the reaction solution is contacted with the solid support. The amount of analyte is then determined by measuring by a label-free mass-detection technique, such as surface plasmon resonance, the amount of binding partner immobilized on the solid support via the reacted conjugate. This is made possible by the binding partner having a considerably greater mass than the conjugate. Variants of this method are also disclosed.